If you don't have any duplex paper from an old roll to measure it out carefully, just look at any 6x6 or 6x9 camera. Borrow and measure yourself. It's not as trivial, as people may seem.

My pressure plate (Moskva 5) is 90.8 mm x 62.9mm, holes have 12mm diameter with red windows closer to 10mm diameter.
If I start measuring from the corner of the plate where my winding knob is (top right part of the camera looking from the lens side or "front"), I'm getting the following:
6x6 hole center: 36.3 mm horizontally, 31.6mm vertically
6x9 hole center: 76.5 mm horizontally, 49.3mm vertically
possible error would be up to 1 mm, but I hope it's close enough.